1. Field of the Invention
This invention relates to rotary fluid devices, and more particularly to a rotary fluid device of the sliding vane type. The term, "fluid device", as used herein, may be taken to mean any apparatus for converting between mechanical and fluid power, and encompasses fluid pump and/or fluid motor devices.
2. Description of the Prior Art
Rotary fluid devices of the sliding vane type are well known, and are typified, inter alia, by three prior art references, described below.
A first type of rotary fluid device is described in U.S. patents to Erickson (U.S. Pat. No. 3,586,466) and to Rosen (U.S. Pat. No. 2,393,223). In general, a right circular cylindrical rotor is rotatably and concentrically mounted in a cylindrical chamber formed in a housing. Portions of the cylindrical chamber wall conform to the cylindrical rotor periphery, while other wall portions are enlarged in a direction away from the rotor axis to define pressure chambers between the rotor periphery and the enlarged chamber wall portions. The rotor contains plural radial slots at regular intervals through its periphery. A generally planar vane is slidably held in each slot so that the opposed end edges of each vane are coincident with the ends of the rotor. These opposed end edges and the rotor ends are in continuous, sliding and sealing engagement with end caps which close the chamber. The vanes are radially slidable in the slots toward the axis of rotor rotation, until an outer edge thereof is coincident with the cylindrical rotor surface, when they are opposite the conformal portions of the chamber wall. When the vanes are opposite the enlarged portions (i.e., in the pressure chambers) of the chamber wall, they are free to slidably move away from the rotor axis until their outer edges abut the surface of the enlarged portions. A pair of passages communicate with each pressure chamber and means are provided for urging the vanes radially outwardly to maintain their outer edges in constant contact with the chamber wall. Thus, between each vane a variable volume pressure cell is formed, the volume of which varies as the rotor rotates and the cells are successively moved through the pressure chambers.
In use as a motor, one passage in each pressure chamber is connected to a source of fluid under pressure, the other to a low pressure fluid reservoir. The outwardly urged vanes are acts on by the fluid as it moves from the one passage to the other to exert a rotative force on the rotor. As a pump, the rotor is turned to increase and then decrease the volume of the cells. As the cell volume increases, one passage of the pair communicating therewith experiences decreased pressure to remove a quantity of fluid from a reservoir. Subsequently, as the cell volume decreases, the fluid is forced out of the other passage.
The vane urging means may comprise channels in the rotor, in the end caps and/or in the housing for selectively applying high pressure fluid to the vanes within the slots in the rotor. Moreover, a similar means may be provided to selectively apply radially inward forces to the vanes to prevent too great frictional forces between the vanes and the chamber wall which can cause "banging" or rough operation.
A second type of fluid device typified in Barriger (U.S. Pat. No. 120,231) is similar, except that inward and outward radial sliding of the vanes is purely mechanical, being effected by tenons or cam followers formed on the vanes which ride in cam slots formed in the end caps. Here, the pressure chamber may or may not have enlarged portions, pressure cells being defined in any event between adjacent, outwardly moved vanes.
It has been found that the majority of fluid devices constructed in accordance with the prior art, described above, do not usually satisfactorily operate as motors in high torque, low speed modes. Consequently, the use of such fluid devices as motors requires the gearing down of the shaft speed which adds to overall cost. Moreover, many of the prior art fluid devices do not satisfactorily operate as both motors and pumps. Consequently, certain fluid systems involving both fluid motor and fluid pump functions require the use of two fluid devices again adding to total cost.
Moreover, because of the radially inward and outward movement of the vanes, the total size of prior art fluid devices is rather large compared with the size of the rotors. Specifically, the inward and outward sliding movement of the vanes requires that the pressure chamber have a certain maximum diametrical dimension sufficiently large to accomodate the outwardly moved vanes. Because of the high pressures involved and because the housing for the chambers requires a certain amount of mechanical strength, this large diametric size of the chambers leads to the large, cumbersome size of the present fluid devices.
Additionally, the facilities described above for maintaining the vanes in contact with the chamber walls (and for counterbalancing this maintenance force to prevent a drastic increase in frictional forces) are often quite complicated. This complication again adds to the total cost of such a fluid device. However, if such facilities are not present, the vanes, not being positively controlled in their movement against the chamber walls, will often "skip" at high speeds. The Barriger-type of motor partially avoids "skipping", but as other types of prior art fluid devices, is quite physically large because of the need to accommodate inward and outward vane movement beyond the periphery of the rotor.